Due to its high rotational precision and calmness, a fluid dynamic bearing device can be suitably used in a spindle motor for an information apparatus, such as a magnetic disk drive like an HDD, an optical disk drive for a CD-ROM, CD-R/RW, DVD-ROM/RAM or the like, or a magneto-optical disk drive for an MD, MO or the like, a polygon scanner motor of a laser beam printer (LBP), a motor for a projector color wheel, or a small motor, such as a fan motor for cooling an electrical apparatus or the like.
For example, in the fluid dynamic bearing device disclosed in Patent Document 1, a radial bearing gap is formed between an outer peripheral surface of the shaft member and an inner peripheral surface of a sleeve portion, the shaft member being supported in a radial direction with a fluid film generated in the radial bearing gap and being supported in a thrust direction by bringing a spherical protruding portion provided at a lower end portion of the shaft member and a thrust plate provided on an inner bottom surface of a housing in sliding contact with each other. Further, in the fluid dynamic bearing device, the shaft member includes a smaller diameter portion and a larger diameter portion so as to exhibit a stepped shape, and an annular seal portion is provided on an inner periphery of an opening portion of the housing. The seal portion is engaged with a shoulder surface of the shaft member in an axial direction so as to retain the shaft member.    Patent Document 1: JP 2005-113987 A